Leveraging Macromolecular Isomerism for Phase Complexity in Janus Nanograins

It remains intriguing whether macromolecular isomerism, along with competing molecular interactions, could be leveraged to create unconventional phase structures and generate considerable phase complexity in soft matter. Herein, we report the synthesis, assembly, and phase behaviors of a series of precisely defined regioisomeric Janus nanograins with distinct core symmetry. They are named B2DB2 where B stands for iso-butyl-functionalized polyhedral oligomeric silsesquioxanes (POSS) and D stands for dihydroxyl-functionalized POSS. While BPOSS prefers crystallization with a flat interface, DPOSS prefers to phase-separate from BPOSS. In solution, they form 2D crystals owing to strong BPOSS crystallization. In bulk, the subtle competition between crystallization and phase separation is strongly influenced by the core symmetry, leading to distinct phase structures and transition behaviors. The phase complexity was understood based on their symmetry, molecular packing, and free energy profiles. The results demonstrate that regioisomerism could indeed generate profound phase complexity.

S3 using a TA Instruments under nitrogen atmosphere with a heating rate of 10 ℃ min -1 to obtain their melting temperature and the crystallization temperature. Size exclusion chromatography (SEC) results were performed on a Viscoteck SEC 270maxTM (Malvern, U.K.). The samples were dissolved in THF with the concentration of 2 mg mL -1 and THF was also used as eluent (flow rate: 0.10 mL min - images and selected area electron diffraction (SAED) experiments were recoded using the same S4 equipment.

Sample Preparation
Crystalline samples of B2DB2 for X-ray experiments were prepared by first dissolving about 100 mg samples in a THF/MeCN (v/v = 1/1) mixed solvent. The solution was then allowed to slowly evaporate at room temperature to give bulk powder samples, which were further dried in vacuo overnight at 60°C. The dried powder samples were sealed into an aluminum sample holder with a hole of 2 mm diameter for SAXS and WAXS measurements. Powder samples treated by the same procedure were also transferred to an aluminum DSC pan with a weight of about 2 mg for DSC measurements.
To prepare thermally annealed samples at higher temperatures, paraand ortho-isomer were directly annealed at 190 °C for 2 h, meta-isomer was first heated to 200 °C with a heating rate of 30 °C/min, then followed by immediate cooling to 178~182 °C and then annealed for 0.5-24 h. All thermal annealing procedures were performed under vacuum. After cooled to room temperature, the samples were used in SAXS and WAXS measurements. Noted that once the mesophases were formed (Colh for para-, iColh for meta-, and A15 for ortho-isomers), slowly cooled to room temperature or quenched in liquid nitrogen will form the same structure. At this stage, phase separation will dominate the structure, the crystallization of BPOSS is restrained.
Once the ordered structures were formed, they were immediately quenched into the liquid nitrogen and microtomed for transmission electron microscopy (TEM) observations. Thin slices of the bulk samples suitable for TEM experiments were obtained using a Reichert Ultracut S (Leica) microtome on annealed samples embedded in epoxy monolith at room temperature. The slices were transferred to carbon coated copper grids for TEM experiments. The thickness of these thin slices was around 70-100 nm. When necessary, staining of the samples was performed at room temperature by using RuO4 for 10 min. After BF TEM images were obtained, the experimental SAED patterns were S5 then taken at the same area of the microtomed sample. The d-spacings were calibrated using a TlCl standard.                 . 29 Si NMR spectrum of ortho-B2DB2 and the peak analysis, the integral area of peak 1 and 2 is 1.74:1 which is approximately 2 to 1.

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Section II. Molecular Self-assemblies. Figure S6. Synchrotron X-ray scattering patterns of para-B2DB2 at the small (left) and wide (right) angle regions. Figure S7. Selected area electron diffraction (SAED) pattern of para-B2DB2 along <001> direction of hexagonal lattice from Figure 3D. Figure S8. Dark field TEM image of para-B2DB2 annealed at 175 °C using the same sample imaged in Figure 3D.    Figure S11. SAXS pattern of ortho-B2DB2 after forming the A15 phase at 190 °C then cooling down to 40 °C (10 °C/min), the A15 phase will not translate to hexagonal crystal while the crystallinity of BPOSS is also very low with only one peak at ~ 5.7 nm -1 . The temperature was hold for at least 30 min per interval. Asterisks at ~ 5.5 nm -1 are noisy points of some bad pixels from the detector.  For Colh, where d is the columnar diameter in Colh lattices, r is the selected space (1 nm), ρ is the density of the sample (1.24g/cm 3 for para-isomer and 1.22g/cm 3 for meta-isomer), M is molecular weight of sample and NA is the Avogadro's number.
Average cross-section area per molecule (A0): For Colh, the cross-section area (A0) can be calculated as: where R is the intercolumn distance of Colh ( = 2 1
For A15, where D is the average diameter of DPOSS aggregates in each sphere of the A15 lattice and a is the lattice parameter of A15.
Full indexation and lattice parameters of hexagonal phase may be determined by solving Eq. S9: Eq. S9 the indexation is listed in Table S1-3.
Full indexation and lattice parameters of cubic A15 phase may be determined by solving Eq. S10: Eq. S10 The indexation is listed in Table S4. 2.34 † Peak positions from SAXS data. ‡ Expected peak positions for assigned space group with given lattice dimensions.